Various types of gas discharge tubes are known for providing light in the visible and invisible portions of the electromagnetic spectrum. Generally, a gas discharge tube requires a high voltage during a starting phase to initially ionize or excite gas molecules within the tube and, once a plasma of ionized gas molecules is created, a lower voltage to run the tube.
One form of device for starting and running gas discharge tubes is a regulating transformer, such as a model number SCT-1 available from Ultra-Violte Products, Inc. A regulating transformer provides an initial high starting voltage to ignite the tube and a lower tube running voltage. However, such transformers have several disadvantages. They are often large and heavy, produce radio frequency interference (RFI) which may be difficult to shield or otherwise isolate, and generate excessive heat.
In an effort to overcome the disadvantage associated with such transformers, it is known to use a DC inverter to provide AC starting and running voltages to a gas discharge tube. Such an inverter includes a transformer having primary and secondary windings and is self oscillating such that the input DC current is conducted in an alternating fashion through the transformer primary winding. As is well known, the ratio of the number of turns on the transformer primary winding to the number of turns in the transformer secondary winding is proportional to the voltage step-up or step-down produced by the transformer.
Prior DC inverters used to operate a gas discharge tube develop a high AC starting voltage by applying input DC current to a first tap on the primary winding of the transformer connected to provide a high voltage step-up. The input DC current is applied for a predetermined time during which the tube ignites. After the predetermined time, the input DC current is applied to a second tap on the transformer primary winding, the second tap providing a lower voltage step-up and thus providing a lower AC running voltage for the tube.
Although such DC inverters are generally more efficient than a transformer, and thus generate less operating heat, can be better shielded to prevent RFI and can be adapted to fit where a transformer may not be used, such inverters can draw high undesirably input DC currents during the predetermined high voltage output time since the tube is partially conductive during at least a portion of such time. Thus, the high current demand required to start the tube requires that the converter include heavier transformer windings, transistors with higher current ratings and other components suitable for high current flow through the inverter. Moreover, such high current flow produces unwanted heat and requires that the power supply providing input DC current for the inverter be capable of supplying high currents during the starting phase of tube operation.
Thus, there is a need for a device for starting and running gas discharge tubes which does not require large currents during the tube starting phase, consequently decreasing the need for a large input DC power supply and allowing the use of components with lower current ratings. Moreover, there is a need for a tube starting and running device which dissipates less heat during the tube starting phase than prior inverter devices.